Wilcox's 1859 Hot Air Engine patent # 23,876

Source : United States Patent Office
Title: Air Engine
Inventor : Stephen WIlcox, Jr., of Westerly, in the county of Washington and State of Rhode Island
Date: May 3, 1859
Patent #: 23,876


To all whom it may concern:

Be it known that I, STEPHEN WILCOX, Jr., of Westerly, in the county of Washington and State of Rhode Island, have invented certain new and useful Improvements in Hot-Air Engines, and that the following is a full, clear, and exact description thereof, reference being had to the annexed drawings and to the letters of reference marked thereon, in which—
The Wilcox hot air engine of 1859 - Fig. 1
The Wilcox hot air engine of 1859 - Fig. 2
The Wilcox hot air engine of 1859 - Fig. 2a and 3
The Wilcox hot air engine of 1859 - Fig. 4 and 5
The Wilcox hot air engine of 1859 - Fig. 6 to 13
The Wilcox hot air engine of 1859 - Fig. 14
Figure 1 is a vertical longitudinal section through the whole engine. Fig. 2 is a plan view of the same. Fig. 3 is a horizontal section through the regenerator. Fig. 4 is an elevation of the valve gear. Fig. 5 is a plan of the same. Figs. 6, 7, 8, 9, 10, 11, 12, and 13, are outline figures showing the relative positions of the valve and working pistons and the relative temperatures and pressures of the air at various points in a complete revolution. Fig. 14 is a diagram similar to those produced by what is known as an “indicator.”

Similar letters of reference denote like parts in all the drawings.

The general form of my engine somewhat resembles that invented by Robert Stirling and patented in England in 1840, and 1827.

The nature of my invention consists firstly 30 in a manner of combining and arranging the pistons and the means of effecting the induction and education of air in the two cylinders, whereby one of the pistons serves both as a means of changing the air from the cold to the hot end of the cylinder, and also as a means of supplying a fresh measure of air to be used in the next stroke, with an advantage which will be fully shown below. Secondly, in regulating the temperature of the heating surfaces by the employment of a chamber and diaphragm so arranged relatively to the heating surfaces and the damper in the smoke flue, that the rate of combustion in the furnace is thereby increased and diminished to keep the surface face as a uniform temperature. Thirdly, in so constructing the regenerator that it, shall gradually increase in area from the cold to the hot side, whereby the resistance to the passage of the air is reduced. Fourthly, in combination with two pistons operating in the manner described, so constructing and operating a single valve in a chamber connecting with the cylinders and the external air, that one valve performs the several effects of an induction, education, and equilibrium valve.

To enable others skilled in the art to make and use my invention, I will proceed to describe its construction and operation.

A is the working cylinder and a the single acting working piston. .
B is the changing and supply cylinder, and b the piston working therein.
C is the main shaft supported by the frames r r’ and having two cranks C’ and C’’ set at nearly right angles with each other.

C’’ is a fly-wheel.

D is the valve box communicating freely with E and having three ports d d' d''. Within this is the valve M.

E is a small chamber containing a regenerator F resting upon a central cone f. At the lower end of E are two nozzles e and e' which connect with a nozzle upon each of the cylinders A and B as represented, and form a communication between E and both cylinders. The lower portion of the cylinders A and B and of the chamber E form the heating surfaces.

H is a small cylinder filled with mercury and connecting through tube h with a chamber covered by a diaphragm L. A lever l connects with a crank on the shaft of damper n the effect of which will be explained farther on.

The bed plate is denoted by X.

J is the brick work.

A and B are supported near their centers by a flange resting on X their lower ends projecting into the flue below to receive the heat of the furnace. A is open at its upper end, while B is closed by a tight head. Pistons a and b are made somewhat longer than their stroke, and filed with some nonconductor to prevent the heat to which their lower sides are exposed from being communicated to their upper sides. a has a long pitman a' connecting directly with crank C' while piston b has a rod b' passing through a stuffing box S and having a crosshead b''. A short pitman b''' connects thence with crank C''

The valve M is turned accurately to fit the interior of box D, and has a hollow throat of sufficient width to span ports d' and d'', and the space between them, as shown at Fig. 7. This valve receives an oscillating or partially rotating motion as follows. The axis of M passes through the head of D and has a slotted lever m on its end. (See Figs. 4 and 5.) In the slot plays a roller i carried on idle lever I which is in turn moved by the eccentric rod g.

The regenerator F is a cylinder of wire cloth, its internal diameter is of the same area as the ports in D and the external diameter greater according as the thickness of the regenerator is increased. The object of making the regenerator in this form, is, that as the course of the cold air is from the center of the regenerator outward, and the air commences to receive heat and expand immediately upon entering the regenerator and constantly receives more heat until it escapes at the periphery much increased in volume, it is evident that the area of passage-way should increase from the cold to the hot side. This is effected by my construction of the regenerator, the outside of the wire cylinder, (see Fig. 3) being about double the circumference of the inside and giving an area of passage way proportioned to the bulk of the air at all points whether its motion from the cold side to the hot or in the reverse direction.

Within the regenerator is a cone f filling it at the bottom and coming to an apex on a line with its top, thereby giving a large area for the air to pass at the top, and as the air flows off laterally through the regenerator a less area is required below. The taper of the cone f gives the proper area at all points and allows no more vacant space than is absolutely required. For the same reason the chamber E tapers outwardly from the top to the bottom of the regenerator.

H is a small cylinder resting upon the bottom of E so as to be heated as nearly as possible to the same temperature as the metal upon which it lies. From H a small tube h passes upward through f, thence through the side of D and. connects with the chamber below the diaphragm L. Upon L rests a small plate having a rod connecting with l. From the end of l a link n' connects with a crank on the end of the shaft of damper n in the flue o. This portion, of the engine is of very great practical importance as the change of the structure of the metal in consequence of its being too intensely heated has caused the failure of many otherwise successful air engines.

It must be observed that the vessel H is not immersed in the Products of combustion, and that the motion of the diaphragm L lever I and damper n does not necessarily, and should not in many instances, correspond with the fluctuations in the heat of the fire. The vessel H is within the chamber E and in contact with the inner side of the heating surfaces at its base. Now the heat of the products of combustion is only one of the elements which go to control the temperature of H, the other is the power with which the engine is working. If the engine is working very moderately and with little or no load the temperature of H may rise very nearly to the same point as that of the products of combustion, but when it is working under the opposite conditions the large quantity of air which is to be warmed in any given period tends to cool the interior of the heating surfaces and in order to maintain a uniform heat in the metal requires the temperature on the exterior to be considerably higher than before. The apparatus therefore is intended to maintain a uniform temperature, not in the gases either on the exterior or interior, but in the metal of the heating surfaces, and to produce this result by so adjusting the damper n as to supply just sufficient heat from the fire under all conditions. This feature of my invention is especially important when the engine is frequently stopped, as without it the metal is liable to become heated to a bright red heat in a short time and again to become too much cooled when the engine is started again. .

The furnace K is supplied with fuel through door P; the brick work J extends over the fire and shields the bottoms of the cylinders from the direct radiation of the fire. The products of combustion pass from the furnace and circulate around the bottoms and sides of the cylinders and finally escape to the chimney through flue O.

Although the operation of an ordinary Stirlmg engine, on which my improvements are based, is tolerably familiar to those skilled in the art, it may be proper to explain that the expansive power of heated air is rendered available therein by so operating a working and changing piston in separate cylinders that the changing piston rapidly transfers a measure of air f rom its cold to its hot side, and then stands nearly stationary while the working piston is forced up by the expansion of the heated air, thereby imparting motion to the engine. The changing piston then proceeds to transfer the same air back from the hot to the cold side of the pistons in which transfer it is passed through a refrigerator and its heat is therein abstracted. By this means the pressure of the air is very greatly reduced and the working piston is therefore allowed to descend with comparatively little resistance.

In my engine, as in Stirling’s, a measure of air is transferred from the cold to the hot side of the changing piston and by its expansion the working piston is forced up and power is imparted to the engine. But at or about the termination of the up stroke of the working piston the difference becomes apparent, for at this juncture my valve D by its rotation opens the education port d and allows the hot air to escape, while it also opens the induction port d'. As the changing piston descends, the space above it is filled by a supply of fresh (or relatively fresh) air, drawn either from the atmosphere or from a cool reservoir. When my engine is worked with the air at only about the atmospheric the fresh air is drawn directly from the atmosphere, as represented and the hot air beneath the two pistons is discharged and blown away. But it can if desired be worked in the same manner under a higher pressure, by connecting a strong reservoir (not represented) with both the education and induction ports d and d''. In such case air is compressed by a pump (not represented) until it fills the reservoir to any pressure desired, and the pressure within the engine will correspond therewith, and thus produce a greater effect at each stroke; but when worked in this manner my engine must be provided with a refrigerator, analagous in structure (though not in arrangement and effect equivalent) to Stirling’s. My engine differs from Stirling’s in the following points, viz: Stirling’s alternately transfers the same air from the cold to the hot side of the changing piston and vice versa, while mine discharges the hot air and draws in a supply of other air at each stroke. Stirling’s involves a loss of space in the refrigerator which is analogous in effect to that caused by what is known as “clearance” in steam engineering which loss mine avoids because when the ports d and d' of my engine communicate with the atmosphere no refrigerator is employed and when they communicate with a reservoir of compressed air the refrigerator is outside of or beyond the valve, and its pipes, etc., are a portion of the reservoir and not a portion of the space within the cylinders. The space involved in the refrigerator is not therefore equivalent to clearance in my engine and is of no effect whatever on the same.

The peculiar motions of the two pistons in relation to each other could be effected very perfectly by means of cams, but cranks afford a smoother motion and allow of more rapid action from the tightness at which the parts can be maintained and the very gradual manner in which the changes occur. For this reason I use two cranks C' and C'' placed at nearly right angles on shaft C.
The relative motions imparted to the pistons by the cranks is best shown by Fig. 2^ in which the circle of the crank is divided into four parts. Let crank C’ be at 1 and crank C'' at 2; now if shaft C is turned to the right one fourth of a revolution, C' will be at 2 and C'' at 3 and the piston attached to crank C’ will have passed through about three fourths of its stroke, while the piston attached to crank C” will have moved up and down through one eighth of its stroke. During another fourth of a revolution C' will move up and down through one eighth of its stroke, while C” will pass through its three fourths, thus it will be seen that the cranks give very nearly the desired motions.

Figs. 4 and 5 show the valve gearing. The valve M is mounted on a spindle M’ keyed to which is a slotted lever m. I is an idle link driven by eccentric rod g and turning on a fixed stud t. A roller ‘i is mounted on this lever. The spindle M’ and stud t are not in the same horizontal plane, t being higher than M’, and as lever I vibrates nearly equal distances each side of a horizontal line passing through the center of stud t it. follows that roller I will play longer in the slot during the upward than during the downward stroke, as shown by the dotted lines; it will also be seen that only a slight motion is imparted to the valve except in the middle of the stroke of the eccentric when the valve will be moved rapidly from one extreme position to the other; also that the valve requires to be turned in the upward position about two thirds of the time, and in the downward about one third and to be rapidly transferred from one position to the other. These peculiar motions are effected by the combination of the eccentric with the link and slotted lever. The vessel H is filled with some fluid that vaporizes at a high temperature, as mercury, which will commence evaporating at 650o. When this temperature is attained a portion of the fluid will be forced through tube h raising diaphragm L and lever l by which the damper n is closed, the combustion in the furnace is checked, and the temperature of the heating surfaces is reduced. As the temperature falls a portion of the vapor is condensed and the diaphragm L sinks until the damper n is again opened and the fire quickened. Thus the temperature of the heating surfaces is uniformly maintained at about the point the metal can safely bear.

Having explained the several parts I will proceed to consider the machine in operation. By referring to Figs. 6, 7, 8, 9, 10, 11, 12 and 13, the position of the pistons and valve at each eighth of a revolution can be seen. The circle above each diagram showing the position of the cranks, crank C’ carrying working piston a, and crank C” carrying changing piston b. The pressure of the air in the cylinders is denoted in each diagram by the small figures. These figures may not be strictly correct but will suffice to illustrate the mode of operation. Suppose the parts in commencing be in the position shown by Fig. 6. Piston a has nearly completed its up stroke, piston b has just commenced its clown strobe, and the induction and education ports have commenced to open. If now the main shaft is turned to the right, one eighth of n revolution, the various parts will have assumed the position shown in Fig. 7; piston a has completed its up stroke and piston b has moved down half its stroke, drawing in a supply of cold air to fill the space above it and forcing the hot air beneath it; out through the regenerator, where it leaves a large portion of its, heat and then escapes through the exhaust port. At the next eighth of a revolution, see Fig 8, piston a has commenced its down stroke and piston b has nearly completed its down stroke. At or near this point valve M closes both the induction port d’ and eduction port d and opens a communication through cylinder port d'' between the upper side of b and the lower side of both a and b. At the next position, see Fig. 9, piston a has moved down half stroke, and piston b is at the bottom of its stroke. In Fig. 10 piston a has nearly completed its down stroke,— having forced the hot air beneath it up through the regenerator and out through the port d during the early part of its downward, motion and compressed it with the air above b during the later portion. This compression of course requires considerable power and necessitates a heavy or quick running fly wheel, but it greatly increases the pressure during the up stroke, and serves to overcome the momentum of the parts, having in this respect the same effect as cushioning by the early closing of the exhaust in steam engines. In this figure, piston b has just commenced its up stroke. In Fig. 11, a has completed its down stroke and piston b has moved np half stroke. In Fig. I2 a has commenced and b has nearly completed its up stroke, and the latter has driven the cold air which was above it down through the regenerator absorbing the heat previously treasured in its metal. Thence it flows in contact with the hot surface below and fills the space beneath both a and b at a greatly increased pressure and temperature as indicated by the figures. In Fig. 13, a has been forced by the pressure below it through half its up stroke b being at the end of its up stroke. At the next eighth the revolution is completed and the parts have again assumed the position shown in Fig. 6, a having nearly completed its up stroke and b just commenced its down stroke, and the exhaust and induction ports being just opening. .

Fig. 14 is a diagram intended to show approximately the pressure on the under side of the working piston, and consequently on both sides of the changing piston, at all points in the stroke. The elevation of the red figures 6, 7, 8, 9, 10, 11, 12, 13, and the accompanying figures in black, show the pressure under the piston in the several positions shown by the corresponding figures ; i.e. Fig. 6, Fig. 7, etc. The lines extending from 11, 12, 13, 6, 7, to the base of the diagram, show the pressure under the piston a during the up stroke, the shorter lines extending from 7, 8, 9, 10, 11, to the base show the pressure (adverse) during the down stroke. The line joining 11, 12, 13, 6, 7, is higher than the corresponding one joining 7, 8, 9, 10, 11, and the area between these lines indicates, in a manner familiar to steam engineers, how much more power is derived from the up stroke of piston a than is lost in the return stroke of the same.

In this engine it is seen that the pressure acts only in one direction to force the piston up; we must therefore depend upon the momentum of the fly wheel to complete the downward stroke against a pressure which rapidly increases toward the termination of the motion, but by obvious means two changing pistons and cylinders might be combined with two corresponding working pistons and cylinders in the same manner as here represented so as to form a double acting engine.

The advantages due to my invention are as follows: First, I dispense with pumps and coolers and at the same time run at high speeds without noise. Secondly, the heat regulator or limiter protects the heating surface from the destructive effects of an extreme high temperature and regulates the fire so as to keep the interior of the heating surfaces at a nearly uniform degree of heat under all conditions. Third, the area of passageway through the regenerator is proportioned to the bulk of the air at all points, and the resistance to the passage of the air is thereby much reduced. Fourth, the valve moved as described performs the threefold office of induction, eduction, and equilibrium valve with less friction and less liability to derangement than any means previously known and (what is very important) without involving a necessity for as much air space within the passages.

Having thus fully described my invention and the advantages thereof, what I claim as my invention and desire to secure by Letters ‘Patent is—

  1. The within described arrangement of the changing cylinder B and working cylinder A and the valve or valves by which piston b is made both to change the air from the cold to the hot end of the cylinder, and to receive a fresh volume of air for the next stroke with the advantages within set forth.

  2. Automatically regulating the temperature of the interior of the heating surfaces by the employment of the parts H and L arranged relatively to the heating surfaces of the cylinders A and B, and to the damper n or its equivalent, in the flue O as within described.

  3. Giving the regenerator an increasing area from the cold to the hot side, substantially as and for the purpose herein set forth.

  4. Working the single valve M in combination with the two pistons a and b, as described so as to thereby accomplish the three fold purpose of induction, education and equilibrium valve, substantially in the manner and with the advantage herein set forth.


In presence of